脈沖激光沉積制備ZnO基量子阱及其光學(xué)性質(zhì)研究
發(fā)布時(shí)間：2018-10-19 10:54
【摘要】：作為一種寬帶隙Ⅱ-Ⅵ族氧化物半導(dǎo)體,ZnO被認(rèn)為是光電子產(chǎn)業(yè)的一種有希望的候選材料,在藍(lán)光/紫外(UV)波段有著廣闊的應(yīng)用前景。因?yàn)榧ぷ咏Y(jié)合能高達(dá)60 meV,ZnO的吸引力主要表現(xiàn)在激子室溫穩(wěn)定性方面,這對于半導(dǎo)體器件,如發(fā)光二極管(LEDs)、二極管激光器、紫外探測器等的應(yīng)用均具有十分重要的意義。例如,人們預(yù)測ZnO中激子復(fù)合產(chǎn)生的激射甚至可以出現(xiàn)在室溫以上。在設(shè)計(jì)和制作光電子器件的進(jìn)程中,需要制備高質(zhì)量的ZnO基異質(zhì)結(jié)和量子阱結(jié)構(gòu),因?yàn)榱孔酉抻蛐?yīng)可以有效提高器件的發(fā)光效率。本博士論文以ZnO基多量子阱(MQWs)為中心,主要探討了ZnO基MQWs的制備、結(jié)構(gòu)和光學(xué)性質(zhì),涉及光致熒光(PL)、量子限域效應(yīng)以及熱穩(wěn)定性。主要研究成果總結(jié)如下：(1)通過優(yōu)化ZnO和ZnMgO單層膜在c軸藍(lán)寶石基片上的生長條件,利用脈沖激光沉積(PLD)方法成功地制備出了具有明確多層結(jié)構(gòu)的10個(gè)周期的ZnO/ZnMgO多量子阱。量子阱的阱層厚度在1.4到3.0 nm之間變化。在325 nm的He-Cd激光激發(fā)下,所有的量子阱樣品在室溫下均發(fā)射出強(qiáng)的紫外熒光。量子限域效應(yīng)導(dǎo)致熒光光子的能量在3.38到3.52 eV之間變化。此外,在ZnO/ZnMgO量子阱的PL光譜中,首次觀察到極度增強(qiáng)的多聲子Raman散射(RRS)現(xiàn)象。光譜分析表明,增強(qiáng)的RRS可以歸因于激發(fā)光和發(fā)射光與量子阱中ZnMgO壘層之間的能量共振,即入射共振和出射共振引起的多聲子Raman散射的增強(qiáng)。另一方面,量子阱和ZnMgO單層膜中多聲子Raman散射高度吻合,表明量子阱壘層與相同條件下生長的ZnMgO單層膜具有相同的成分,這可以看作是ZnO/ZnMgO量子阱具有明確多層結(jié)構(gòu)的有力證據(jù)。利用ZnMgO單層膜的PL光譜及通過多聲子RRS確定的縱光學(xué)聲子的能量,估算出ZnMgO壘層中MgO的含量約為15%,進(jìn)而計(jì)算出ZnO和ZnMgO之間導(dǎo)帶和價(jià)帶的偏移量分別為338和38 meV。在此基礎(chǔ)上,根據(jù)Kronig-Penney模型計(jì)算的ZnO/ZnMgO量子阱中的PL位移隨阱層厚度的變化與～12K下的實(shí)驗(yàn)光譜結(jié)果一致。此外,實(shí)驗(yàn)結(jié)果表明,ZnO/ZnMgO量子阱在退火溫度低于600°C時(shí)是穩(wěn)定的；當(dāng)退火溫度提升至700℃以上時(shí),量子阱中ZnO/ZnMgO多層結(jié)構(gòu)將被破壞。(2)作為熒光殺手,Co2+離子摻雜到ZnO中將導(dǎo)致激子復(fù)合熒光的淬滅,但熒光淬滅的物理機(jī)制是一個(gè)懸而未決的問題。在本工作中,首次利用ZnCoO/ZnMgO多量子阱樣品系統(tǒng)研究了Co2+離子摻雜引起的熒光淬滅現(xiàn)象。ZnCoO/ZnMgO多量子阱利用脈沖激光沉積方法生長在帶有～20 nm ZnO過渡層的c面藍(lán)寶石基片上,并表現(xiàn)出與ZnO/ZnMgO多量子阱樣品相似的多聲子RRS增強(qiáng)現(xiàn)象,證明ZnCoO/ZnMgO多量子阱中多層膜結(jié)構(gòu)足夠好,以保證周期性量子阱的形成。與相同條件下生長的ZnCoO單層膜相比,量子限域效應(yīng)導(dǎo)致ZnCoO/ZnMgO量子阱樣品中位于～1.80 eV的Co2+離子熒光增強(qiáng),即量子限域效應(yīng)增強(qiáng)了高度局域化的Co2+3d電子能級的熒光發(fā)射。但是,激子復(fù)合的熒光淬滅現(xiàn)象在ZnCoO/ZnMgO量子阱樣品中仍然存在。因此,Co2+離子摻雜引起的激子熒光淬滅可以確認(rèn)為ZnO激子和局域化的Co2+3d電子態(tài)之間的能量轉(zhuǎn)移,進(jìn)而提出了熒光共振能量轉(zhuǎn)移(FRET)是導(dǎo)致激子熒光淬滅和位于～1.80 eV的Co2+離子熒光增強(qiáng)的物理機(jī)制。(3)在PLD方法制備的具有高外延度的ZnO薄膜中,發(fā)現(xiàn)了一個(gè)異常的具有寬譜特征的光致熒光峰,位于近帶邊(NBE)區(qū)域,PL峰值在～3.0 eV附近。利用變溫PL光譜、PL激發(fā)譜和時(shí)間分辨PL光譜,通過與退火樣品和ZnO單晶樣品的比較研究,這種異常的具有寬譜特征的NBE熒光發(fā)射不能簡單地歸因于某種特定的缺陷。為此,我們提出了一個(gè)帶尾熒光模型。我們認(rèn)為,ZnO薄膜中各種缺陷、化學(xué)無序和晶格應(yīng)變可能會(huì)形成局域化的電子態(tài),位于ZnO導(dǎo)帶以下,形成能帶帶尾。這種異常的NBE熒光發(fā)射正是源于激子在能帶帶尾熱弛豫過程中的輻射復(fù)合。這一物理機(jī)制被時(shí)間分辨光譜和變溫光譜的定量擬合結(jié)果所證實(shí)。此外,發(fā)展了一種管式放電等離子體束流輔助的PLD裝置,用于制備N摻雜ZnO薄膜,并研究了ZnO薄膜的電輸運(yùn)性質(zhì)和光致熒光光譜隨沉積過程中0分壓的變化。
[Abstract]:As a wide band gap II-VI oxide semiconductor, ZnO is regarded as a promising candidate material for the optoelectronic industry, and has a wide application prospect in the blue/ ultraviolet (UV) wave band. Because the exciton binding energy is up to 60 meV, the attraction of ZnO is mainly manifested in the stability of exciton room temperature, which is very important for semiconductor devices such as light emitting diode (LED), diode laser, ultraviolet detector and so on. For example, it is predicted that the triplet state of exciton recombination in ZnO may even occur at room temperature or more. In the process of designing and fabricating optoelectronic devices, high quality ZnO-based heterojunction and quantum well structures need to be prepared because the quantum confinement effect can effectively improve the light-emitting efficiency of the device. The preparation, structure and optical properties of ZnO-based MQWs, including light-induced fluorescence (PL), quantum confinement field effect and thermal stability, are discussed. The main results are summarized as follows: (1) By optimizing the growth conditions of ZnO and ZnMgO single-layer films on c-axis sapphire substrate, a 10-cycle ZnO/ ZnMgO multi-quantum well with definite multi-layer structure was successfully fabricated by pulsed laser deposition (PLD) method. the well layer thickness of the quantum well varies between 1. 4 and 3. 0nm. All quantum well samples emit strong ultraviolet fluorescence at room temperature under the excitation of He-Cd laser at 325 nm. The quantum confinement effect causes the energy of the fluorescent photons to vary from 3.38 to 3.52 eV. In addition, in PL spectra of ZnO/ ZnMgO quantum wells, extremely enhanced multi-phonon Raman scattering (RRS) phenomenon was observed for the first time. The spectral analysis shows that the enhanced RRS can be attributed to the enhancement of the energy resonance between the excitation light and the emission light and the ZnMgO barrier layer in the quantum well, that is, the enhancement of the multi-phonon Raman scattering caused by incident resonance and emission resonance. On the other hand, the multi-phonon Raman scattering height in the quantum well and the ZnMgO single-layer film is consistent, which indicates that the quantum well barrier layer has the same composition as the ZnMgO single-layer film grown under the same conditions, which can be seen as a strong evidence that the ZnO/ ZnMgO quantum well has a definite multi-layer structure. The content of MgO in ZnMgO barrier layer is estimated to be about 15% by using PL spectrum of ZnMgO single layer film and the energy of longitudinal optical phonon determined by multi-phonon RRS, and then the offset of conduction band and valence band between ZnO and ZnMgO is calculated as 338 and 38meV, respectively. On this basis, the PL displacement in the ZnO/ ZnMgO quantum well calculated from the Kronig-Penney model is consistent with the experimental spectral results under ~ 12K. Furthermore, the experimental results show that the ZnO/ ZnMgO quantum well is stable when the annealing temperature is lower than 600 擄 C, and when the annealing temperature is raised above 700 鈩，
本文編號：2280906
[Abstract]:As a wide band gap II-VI oxide semiconductor, ZnO is regarded as a promising candidate material for the optoelectronic industry, and has a wide application prospect in the blue/ ultraviolet (UV) wave band. Because the exciton binding energy is up to 60 meV, the attraction of ZnO is mainly manifested in the stability of exciton room temperature, which is very important for semiconductor devices such as light emitting diode (LED), diode laser, ultraviolet detector and so on. For example, it is predicted that the triplet state of exciton recombination in ZnO may even occur at room temperature or more. In the process of designing and fabricating optoelectronic devices, high quality ZnO-based heterojunction and quantum well structures need to be prepared because the quantum confinement effect can effectively improve the light-emitting efficiency of the device. The preparation, structure and optical properties of ZnO-based MQWs, including light-induced fluorescence (PL), quantum confinement field effect and thermal stability, are discussed. The main results are summarized as follows: (1) By optimizing the growth conditions of ZnO and ZnMgO single-layer films on c-axis sapphire substrate, a 10-cycle ZnO/ ZnMgO multi-quantum well with definite multi-layer structure was successfully fabricated by pulsed laser deposition (PLD) method. the well layer thickness of the quantum well varies between 1. 4 and 3. 0nm. All quantum well samples emit strong ultraviolet fluorescence at room temperature under the excitation of He-Cd laser at 325 nm. The quantum confinement effect causes the energy of the fluorescent photons to vary from 3.38 to 3.52 eV. In addition, in PL spectra of ZnO/ ZnMgO quantum wells, extremely enhanced multi-phonon Raman scattering (RRS) phenomenon was observed for the first time. The spectral analysis shows that the enhanced RRS can be attributed to the enhancement of the energy resonance between the excitation light and the emission light and the ZnMgO barrier layer in the quantum well, that is, the enhancement of the multi-phonon Raman scattering caused by incident resonance and emission resonance. On the other hand, the multi-phonon Raman scattering height in the quantum well and the ZnMgO single-layer film is consistent, which indicates that the quantum well barrier layer has the same composition as the ZnMgO single-layer film grown under the same conditions, which can be seen as a strong evidence that the ZnO/ ZnMgO quantum well has a definite multi-layer structure. The content of MgO in ZnMgO barrier layer is estimated to be about 15% by using PL spectrum of ZnMgO single layer film and the energy of longitudinal optical phonon determined by multi-phonon RRS, and then the offset of conduction band and valence band between ZnO and ZnMgO is calculated as 338 and 38meV, respectively. On this basis, the PL displacement in the ZnO/ ZnMgO quantum well calculated from the Kronig-Penney model is consistent with the experimental spectral results under ~ 12K. Furthermore, the experimental results show that the ZnO/ ZnMgO quantum well is stable when the annealing temperature is lower than 600 擄 C, and when the annealing temperature is raised above 700 鈩，
本文編號：2280906
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